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Purpose <p>Hybrid dosimetry, which combines planar imaging with single time-point SPECT/CT, reduces patient burden while maintaining the accuracy of voxel-based approaches. However, due to pharmacokinetic variability across organs and lesions, the SPECT/CT acquisition time (scale point) can substantially affect estimated absorbed doses. This study aimed to determine the accuracy of various scale points in hybrid dosimetry.</p> Methods <p>We analyzed data derived from SPECT/CT and planar whole-body images acquired from three patients (A, B, and C) at 3–4, 25–30, 95–100, and 120–190&#xa0;h after being injected with <sup>1</sup>⁷⁷Lu-DOTATATE. Information about patients A and B was retrieved from the SNMMI Lu-177 Dosimetry Challenge 2021 dataset (patient B had been treated by splenectomy) and patient C who was treated for multiple liver metastases at our institution. Residence times and absorbed doses were calculated using Hermia Organ Dosimetry™, with each SPECT/CT time point used as the scale point. Reference absorbed doses in the kidneys, liver, spleen, bone marrow, and lesions were obtained from all SPECT/CT images using Hermia Voxel Dosimetry™.</p> Results <p>Absorbed doses in both normal organs and lesions were generally overestimated by planar-based dosimetry compared to voxel-based dosimetry. In hybrid dosimetry, absorbed doses varied with scale point selection, with later scale points tending to yield longer residence times. The highest correlation with voxel-based dosimetry was found at the 95–100&#xa0;h scale point (r = 0.9139). We identified residual discrepancies in specific organs, particularly in patients with tumor infiltration or atypical pharmacokinetics.</p> Conclusion <p>Selection of the scale point in hybrid dosimetry substantially impacted absorbed dose estimates. Accurate dose assessment requires organ- and lesion-specific optimization of the time point when SPECT/CT images were acquired, as it reflects differences in the half-life of the injected radiopharmaceutical.</p>

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Impact of scale point selection on absorbed dose estimation in hybrid dosimetry for 177Lu-DOTATATE therapy

  • 期刊论文

  • 发表日期：

    2025年8月1日

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  • Noriaki Miyaji,
  • Kenta Miwa,
  • Naochika Akiya,
  • Kaito Wachi,
  • Arata Komatsu,
  • Masaki Masubuchi,
  • Kosuke Yamashita,
  • Kei Wagatsuma,
  • Tensho Yamao,
  • Takayuki Yagihashi,
  • Taro Murai

摘要

Purpose

Hybrid dosimetry, which combines planar imaging with single time-point SPECT/CT, reduces patient burden while maintaining the accuracy of voxel-based approaches. However, due to pharmacokinetic variability across organs and lesions, the SPECT/CT acquisition time (scale point) can substantially affect estimated absorbed doses. This study aimed to determine the accuracy of various scale points in hybrid dosimetry.

Methods

We analyzed data derived from SPECT/CT and planar whole-body images acquired from three patients (A, B, and C) at 3–4, 25–30, 95–100, and 120–190 h after being injected with 1⁷⁷Lu-DOTATATE. Information about patients A and B was retrieved from the SNMMI Lu-177 Dosimetry Challenge 2021 dataset (patient B had been treated by splenectomy) and patient C who was treated for multiple liver metastases at our institution. Residence times and absorbed doses were calculated using Hermia Organ Dosimetry™, with each SPECT/CT time point used as the scale point. Reference absorbed doses in the kidneys, liver, spleen, bone marrow, and lesions were obtained from all SPECT/CT images using Hermia Voxel Dosimetry™.

Results

Absorbed doses in both normal organs and lesions were generally overestimated by planar-based dosimetry compared to voxel-based dosimetry. In hybrid dosimetry, absorbed doses varied with scale point selection, with later scale points tending to yield longer residence times. The highest correlation with voxel-based dosimetry was found at the 95–100 h scale point (r = 0.9139). We identified residual discrepancies in specific organs, particularly in patients with tumor infiltration or atypical pharmacokinetics.

Conclusion

Selection of the scale point in hybrid dosimetry substantially impacted absorbed dose estimates. Accurate dose assessment requires organ- and lesion-specific optimization of the time point when SPECT/CT images were acquired, as it reflects differences in the half-life of the injected radiopharmaceutical.